The Footstool

Orion, the hunter, strides boldly across the southern sky on winter nights. The big, bright constellation is low in the east shortly after nightfall, with its famous “Belt” of three bright stars pointing up from the horizon. Orion’s brightest star, blue-white Rigel, is to the right of the Belt, representing the hunter’s foot.

A mighty foot can get mighty tired, so long-ago skywatchers gave Orion a convenient footstool to rest it on — a pattern of four relatively faint stars that’s above Rigel in early evening. The brightest member of the group is known as Cursa, from an Arabic name that means “footstool of the Central One.” It marks the western end of the winding constellation Eridanus, the river.

Like many of the stars that are visible to the unaided eye, Cursa is a stellar giant. It’s nearing the end of its “normal” lifetime, so it’s beginning to puff up, getting brighter as it does so. So even though it’s almost 90 light-years away, the fact that it’s bigger and brighter than the Sun makes it easy to see.

As Cursa undergoes a series of changes in its core, it’ll grow even bigger and brighter. Then it’ll blow its outer layers off into space, leaving behind only its hot but dead core — a white dwarf. Over the eons, that remnant will slowly cool and fade away, shifting the course of the meandering celestial river.

Watch Orion as it climbs across the south during the night, with the footstool rotating below the hunter’s bright foot.

Script by Damond Benningfield, Copyright 2012

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